The need for high quality, low cost, and high productivity in industrial manufacturing and processing demands an increase in the use of automation and the utilization of robots. For an automated process, such as a manufacturing robot, to operate correctly in a given environment, the robot should have a means of determining information about the surrounding environment. For instance, an automated riveting machine on an assembly line should be able to compensate for positional variances in the object that is to be riveted and be able to determine the correct amount of force to apply to place and pop a rivet.
To enable automated processes (e.g., robots) to make determinations about a given environment, the robot should have sensors that are able to sense specific aspects of that environment. For a robotic riveter, the riveter should have sensors that determine the positioning of an object that is to be riveted. In the case where the positioning is improper, there should be further systems (e.g., feedback systems) that use the sensor data to compensate for the positional variations either by repositioning the object that is to be riveted or by repositioning the riveter.
For a sensor to effectively operate in a dynamic environment like an assembly line, the sensor should be able to differentiate between more than just a bi-level state as in an "on" or "off" condition. The sensor should be able to differentiate between graded inputs such as variations in an applied force.
A tactile sensor is a, type of sensor that is widely used in automated industrial processes. A tactile sensor detects a given parameter (e.g., pressure) by actually coming into contact with the object or environment that it is detecting. Tactile sensors may be used to measure not only force but also force distribution and surface texture of objects as the objects come in contact with a piece of automation such as a robotic arm. The tactile sensors may provide the robotic arm with a sense of touch and therefore enable such functions as determining the magnitude of an applied force, determining part orientation, identifying parts, sorting of parts, retrieval of parts (e.g., from a storage bin), etc. Precision tactile sensors may be utilized in numerous other applications. For instance, in the health care field, tactile sensors can be used in devices such as prosthetic gloves for the handicapped to in effect, give the prosthetic glove a sense of touch.
A good tactile sensor should have a high resolution to make determinations about small variations in measured parameters. The sensor should be scalable to enable appropriate sizing of the sensor for a given task. For instance, groups of sensors should be able to be manufactured in a high density so that variations in a sensed parameter can be determined over a small area. The tactile sensor should have a fast response time to enable rapid determinations in a changing environment. Further, the tactile sensor should be stable so that a given sensed parameter, such as an applied force, can be reliably determined.
There are a variety of tactile sensors that are known in the prior art. One prior art tactile sensor uses conductive elastomers as a sense element. The conductive elastomers change resistance when compressed by an applied force. Conductive elastomers cannot be formed as part of a CMOS fabrication process and therefore are not capable of being integrated with on-chip CMOS signal processing. A better approach uses a piezoelectric film as the sense element These tactile sensors utilize a diaphragm as a sensing element, and are relatively simple and inexpensive to fabricate. However, piezoelectric film sensors have poor stability and are difficult to scale to smaller dimensions.
Some other tactile sensors utilize semiconductor integrated circuit ("IC") technology. IC tactile sensors may use a resistive or capacitive device as a sense element. These devices may, for instance, be fabricated using a wet chemical etching of a silicon or polysilicon to form a piezoresistor. Although some prior art methods offer high performance (e.g. stability), most of the methods do not lend themselves easily to large, high resolution arrays since the minimum size of a single sensing cell is too large for very dense applications.
Prior art tactile sensors may not be reliable or stable because a response to a force applied to a sensing cell may vary depending on where, with respect to the sensing cell, the force is applied. This affects the accuracy of the prior art tactile sensors.
Therefore, it is an object of the present invention to utilize a method of manufacturing a tactile sensor, wherein said manufacturing process is simple and inexpensive.
Another object of this invention is to provide a method of manufacturing a tactile sensor that results in a sensor that exhibits a high degree of reliability and stability.
A further object of this invention is to provide a method of manufacturing a plurality of tactile sensors in an integrated circuit, wherein said plurality of sensors may be densely placed together or otherwise appropriately sized and spaced.
A still further object of this invention is to provide an improved sensor that exhibits a high degree of resolution.
A yet further object of this invention is to provide an improved sensor that is reliable, stable and can accurately determine the magnitude of an applied force.